A variety of endoluminal introducer devices is known for deploying prostheses and other implants into the vasculature of a patient. One type of such introducers is designed to deploy a prosthesis or other implant for permanent implantation within a patient. Other types of introducer are designed both to deploy a prosthesis or other implant as well as to retrieve this on the completion of a particular medical procedure. One particular example of this latter type relates to the deployment and retrieval of filters within a body lumen of a patient. Introducers of this type, such as that disclosed in the Applicant's earlier United States patent application US-2005/0222604, includes a stylet provided with a hook at its distal end designed to hook into a loop provided on a filter. The stylet and filter are retained within a catheter during deployment and retrieval of the filter. The arrangement is such that the stylet can be pushed through its holding catheter so as to push the filter out of the distal end of the catheter, at which point the filter expands into its deployed configuration. The stylet can be unhooked from the filter to retain the filter in place during a medical procedure. The filter can be retrieved by hooking the stylet again into the loop of the filter and pulling this back into the holding catheter, upon which it collapses into a configuration analogous to that prior to its deployment.
In order to facilitate the deployment and retrieval operations, it is known for such filter introducer devices to be provided with a spring element, such as a coil spring, which biases the stylet to a retracted position within the holding catheter. An actuator, such as a button at a proximal end of the introducer, can be operated by a surgeon so as to push the stylet out of the holding catheter, against the force of the spring element. Release of the actuator causes the stylet to be pulled back into the catheter under the force of the spring element. Further details of an introducer of this nature are given below in the specific description, in connection with FIGS. 1 and 2.
The provision of a spring element biases the stylet into a retracted position, thus retaining the filter within the introducer device not only during the deployment/retrieval operations but also during transportation and other manipulation of the introducer.
A problem has been found to arise with introducers of the above nature, in that although the spring element normally effectively retains the filter or other device in the introducer, knocks or jolts to the introducer, which can occur particularly during transportation and other manipulation, have been known to cause the stylet to move longitudinally relative to the holding catheter to such an extent that the filter is pushed out of the catheter, unhooking itself from the stylet end and therefore coming loose from the introducer. When this occurs, the introducer assembly becomes unusable.